Life Processes
What the exam tests
Life Processes tests nutrition, respiration, transport, excretion and the coordination of these processes in plants and animals. Questions often ask for the photosynthesis equation, the path of blood, or the difference between aerobic and anaerobic respiration.
Core rules
- Autotrophic nutrition: photosynthesis in chloroplasts uses CO2 and water with light energy: 6CO2 + 6H2O → C6H12O6 + 6O2.
- Heterotrophs may be saprophytic, parasitic or holozoic. Digestion breaks large molecules into absorbable ones.
- Aerobic respiration: glucose + oxygen → CO2 + water + much energy. Anaerobic in yeast gives ethanol + CO2; in muscle it gives lactic acid and less energy.
- Transport in plants: xylem carries water and minerals upward; phloem carries sugars in both directions.
- Human circulation is double: pulmonary and systemic. Arteries carry blood away from the heart; veins carry it back. The pulmonary artery carries deoxygenated blood.
- Excretion: nephrons filter blood in kidneys; urine passes through ureters, bladder and urethra.
- Stomata allow gas exchange and transpiration; guard cells open and close them.
Worked example
A plant is kept in a dark cupboard for two days and then tested with iodine for starch. Explain the result. In darkness, photosynthesis stops, so no new glucose is made and no starch is stored. The leaf does not turn blue-black with iodine. The control leaf kept in light does turn blue-black, showing that light is necessary for photosynthesis.
Traps that cost marks
- Saying phloem carries water; that is xylem.
- Claiming all arteries carry oxygenated blood; the pulmonary artery does not.
- Writing anaerobic respiration in muscles as producing ethanol; it produces lactic acid.
- Forgetting that stomata also lose water vapour, not just exchange gases.